For a definition of the meaning and valid values for WindowBits
refer to the zlib documentation for deflateInit2.

Defaults to MAX_WBITS
.

-MemLevel

For a definition of the meaning and valid values for MemLevel
refer to the zlib documentation for deflateInit2.

Defaults to MAX_MEM_LEVEL.

-Strategy

Defines the strategy used to tune the compression. The valid values are
Z_DEFAULT_STRATEGY
, Z_FILTERED
, Z_RLE
, Z_FIXED
and
Z_HUFFMAN_ONLY
.

The default is Z_DEFAULT_STRATEGY
.

-Dictionary

When a dictionary is specified Compress::Raw::Zlib will automatically
call deflateSetDictionary
directly after calling deflateInit
. The
Adler32 value for the dictionary can be obtained by calling the method
$d->dict_adler()
.

The default is no dictionary.

-Bufsize

Sets the initial size for the output buffer used by the $d->deflate
and $d->flush
methods. If the buffer has to be
reallocated to increase the size, it will grow in increments of
Bufsize
.

The default buffer size is 4096.

-AppendOutput

This option controls how data is written to the output buffer by the
$d->deflate
and $d->flush
methods.

If the AppendOutput
option is set to false, the output buffers in the
$d->deflate
and $d->flush
methods will be truncated before
uncompressed data is written to them.

If the option is set to true, uncompressed data will be appended to the
output buffer in the $d->deflate
and $d->flush
methods.

This option defaults to false.

-CRC32

If set to true, a crc32 checksum of the uncompressed data will be
calculated. Use the $d->crc32
method to retrieve this value.

This option defaults to false.

-ADLER32

If set to true, an adler32 checksum of the uncompressed data will be
calculated. Use the $d->adler32
method to retrieve this value.

This option defaults to false.

Here is an example of using the Compress::Raw::Zlib::Deflate
optional
parameter list to override the default buffer size and compression
level. All other options will take their default values.

$status = $d->deflate($input, $output)

Deflates the contents of $input
and writes the compressed data to
$output
.

The $input
and $output
parameters can be either scalars or scalar
references.

When finished, $input
will be completely processed (assuming there
were no errors). If the deflation was successful it writes the deflated
data to $output
and returns a status value of Z_OK
.

On error, it returns a zlib error code.

If the AppendOutput
option is set to true in the constructor for
the $d
object, the compressed data will be appended to $output
. If
it is false, $output
will be truncated before any compressed data is
written to it.

Note: This method will not necessarily write compressed data to
$output
every time it is called. So do not assume that there has been
an error if the contents of $output
is empty on returning from
this method. As long as the return code from the method is Z_OK
,
the deflate has succeeded.

$status = $d->flush($output [, $flush_type])

Typically used to finish the deflation. Any pending output will be
written to $output
.

Returns Z_OK
if successful.

Note that flushing can seriously degrade the compression ratio, so it
should only be used to terminate a decompression (using Z_FINISH
) or
when you want to create a full flush point (using Z_FULL_FLUSH
).

By default the flush_type
used is Z_FINISH
. Other valid values
for flush_type
are Z_NO_FLUSH
, Z_PARTIAL_FLUSH
, Z_SYNC_FLUSH
and Z_FULL_FLUSH
. It is strongly recommended that you only set the
flush_type
parameter if you fully understand the implications of
what it does. See the zlib
documentation for details.

If the AppendOutput
option is set to true in the constructor for
the $d
object, the compressed data will be appended to $output
. If
it is false, $output
will be truncated before any compressed data is
written to it.

$status = $d->deflateReset()

This method will reset the deflation object $d
. It can be used when you
are compressing multiple data streams and want to use the same object to
compress each of them. It should only be used once the previous data stream
has been flushed successfully, i.e. a call to $d->flush(Z_FINISH)
has
returned Z_OK
.

Returns Z_OK
if successful.

$status = $d->deflateParams([OPT])

Change settings for the deflate object $d
.

The list of the valid options is shown below. Options not specified
will remain unchanged.

To auto-detect and uncompress an RFC 1950 or RFC 1952 data stream (i.e.
gzip), set WindowBits
to WANT_GZIP_OR_ZLIB
.

For a full definition of the meaning and valid values for WindowBits
refer to the zlib documentation for inflateInit2.

Defaults to MAX_WBITS
.

-Bufsize

Sets the initial size for the output buffer used by the $i->inflate
method. If the output buffer in this method has to be reallocated to
increase the size, it will grow in increments of Bufsize
.

Default is 4096.

-Dictionary

The default is no dictionary.

-AppendOutput

This option controls how data is written to the output buffer by the
$i->inflate
method.

If the option is set to false, the output buffer in the $i->inflate
method will be truncated before uncompressed data is written to it.

If the option is set to true, uncompressed data will be appended to the
output buffer by the $i->inflate
method.

This option defaults to false.

-CRC32

If set to true, a crc32 checksum of the uncompressed data will be
calculated. Use the $i->crc32
method to retrieve this value.

This option defaults to false.

-ADLER32

If set to true, an adler32 checksum of the uncompressed data will be
calculated. Use the $i->adler32
method to retrieve this value.

This option defaults to false.

-ConsumeInput

If set to true, this option will remove compressed data from the input
buffer of the $i->inflate
method as the inflate progresses.

This option can be useful when you are processing compressed data that is
embedded in another file/buffer. In this case the data that immediately
follows the compressed stream will be left in the input buffer.

This option defaults to true.

-LimitOutput

The LimitOutput
option changes the behavior of the $i->inflate
method so that the amount of memory used by the output buffer can be
limited.

When LimitOutput
is used the size of the output buffer used will either
be the value of the Bufsize
option or the amount of memory already
allocated to $output
, whichever is larger. Predicting the output size
available is tricky, so don't rely on getting an exact output buffer size.

When LimitOutout
is not specified $i->inflate
will use as much
memory as it takes to write all the uncompressed data it creates by
uncompressing the input buffer.

If LimitOutput
is enabled, the ConsumeInput
option will also be
enabled.

$status = $i->inflate($input, $output [,$eof])

Inflates the complete contents of $input
and writes the uncompressed
data to $output
. The $input
and $output
parameters can either be
scalars or scalar references.

Returns Z_OK
if successful and Z_STREAM_END
if the end of the
compressed data has been successfully reached.

If not successful $status
will hold the zlib error code.

If the ConsumeInput
option has been set to true when the
Compress::Raw::Zlib::Inflate
object is created, the $input
parameter
is modified by inflate
. On completion it will contain what remains
of the input buffer after inflation. In practice, this means that when
the return status is Z_OK
the $input
parameter will contain an
empty string, and when the return status is Z_STREAM_END
the $input
parameter will contains what (if anything) was stored in the input buffer
after the deflated data stream.

This feature is useful when processing a file format that encapsulates
a compressed data stream (e.g. gzip, zip) and there is useful data
immediately after the deflation stream.

If the AppendOutput
option is set to true in the constructor for
this object, the uncompressed data will be appended to $output
. If
it is false, $output
will be truncated before any uncompressed data
is written to it.

The $eof
parameter needs a bit of explanation.

Prior to version 1.2.0, zlib assumed that there was at least one trailing
byte immediately after the compressed data stream when it was carrying out
decompression. This normally isn't a problem because the majority of zlib
applications guarantee that there will be data directly after the
compressed data stream. For example, both gzip (RFC 1950) and zip both
define trailing data that follows the compressed data stream.

The $eof
parameter only needs to be used if all of the following
conditions apply

1

You are either using a copy of zlib that is older than version 1.2.0 or you
want your application code to be able to run with as many different
versions of zlib as possible.

2

You have set the WindowBits
parameter to -MAX_WBITS
in the constructor
for this object, i.e. you are uncompressing a raw deflated data stream
(RFC 1951).

3

There is no data immediately after the compressed data stream.

If all of these are the case, then you need to set the $eof
parameter
to true on the final call (and only the final call) to $i->inflate
.

If you have built this module with zlib >= 1.2.0, the $eof
parameter is
ignored. You can still set it if you want, but it won't be used behind the
scenes.

$status = $i->inflateSync($input)

This method can be used to attempt to recover good data from a compressed
data stream that is partially corrupt.
It scans $input
until it reaches either a full flush point or the
end of the buffer.

If a full flush point is found, Z_OK
is returned and $input
will be have all data up to the flush point removed. This data can then be
passed to the $i->inflate
method to be uncompressed.

Any other return code means that a flush point was not found. If more
data is available, inflateSync
can be called repeatedly with more
compressed data until the flush point is found.

Note full flush points are not present by default in compressed
data streams. They must have been added explicitly when the data stream
was created by calling Compress::Deflate::flush
with Z_FULL_FLUSH
.

$status = $i->inflateReset()

This method will reset the inflation object $i
. It can be used when you
are uncompressing multiple data streams and want to use the same object to
uncompress each of them.

Returns Z_OK
if successful.

$i->dict_adler()

Returns the adler32 value for the dictionary.

$i->crc32()

Returns the crc32 value for the uncompressed data to date.

If the CRC32
option is not enabled in the constructor for this object,
this method will always return 0;

$i->adler32()

Returns the adler32 value for the uncompressed data to date.

If the ADLER32
option is not enabled in the constructor for this object,
this method will always return 0;

The next example show how to use the LimitOutput
option. Notice the use
of two nested loops in this case. The outer loop reads the data from the
input source - STDIN and the inner loop repeatedly calls inflate
until
$input
is exhausted, we get an error, or the end of the stream is
reached. One point worth remembering is by using the LimitOutput
option
you also get ConsumeInput
set as well - this makes the code below much
simpler.

CHECKSUM FUNCTIONS

Two functions are provided by zlib to calculate checksums. For the
Perl interface, the order of the two parameters in both functions has
been reversed. This allows both running checksums and one off
calculations to be done.

If you have built this module with zlib 1.2.3 or better, two more
CRC-related functions are available.

$crc = adler32_combine($crc1, $crc2, $len2)l

$crc = crc32_combine($adler1, $adler2, $len2)

These functions allow checksums to be merged.

Misc

my $version = Compress::Raw::Zlib::zlib_version();

Returns the version of the zlib library.

The LimitOutput option.

By default $i->inflate($input,$output)
will uncompress all data
in $input
and write all of the uncompressed data it has generated to
$output
. This makes the interface to inflate
much simpler - if the
method has uncompressed $input
successfully all compressed data in
$input
will have been dealt with. So if you are reading from an input
source and uncompressing as you go the code will look something like this

The main processing loop in the code handles reading of compressed data
from STDIN.

The status code returned from inflate
will only trigger termination of
the main processing loop if it isn't Z_OK
. When LimitOutput
has not
been used the Z_OK
status means means that the end of the compressed
data stream has been reached or there has been an error in uncompression.

After the call to inflateall of the uncompressed data in $input
will have been processed. This means the subsequent call to read can
overwrite it's contents without any problem.

For most use-cases the behavior described above is acceptable (this module
and it's predecessor, Compress::Zlib
, have used it for over 10 years
without an issue), but in a few very specific use-cases the amount of
memory required for $output
can prohibitively large. For example, if the
compressed data stream contains the same pattern repeated thousands of
times, a relatively small compressed data stream can uncompress into
hundreds of megabytes. Remember inflate
will keep allocating memory
until all the uncompressed data has been written to the output buffer -
the size of $output
is unbounded.

The LimitOutput
option is designed to help with this use-case.

The main difference in your code when using LimitOutput
is having to
deal with cases where the $input
parameter still contains some
uncompressed data that inflate
hasn't processed yet. The status code
returned from inflate
will be Z_OK
if uncompression took place and
Z_BUF_ERROR
if the output buffer is full.

There are now two nested loops in the code: the outer loop for reading the
compressed data from STDIN, as before; and the inner loop to carry out the
uncompression.

There are two exit points from the inner uncompression loop.

Firstly when inflate
has returned a status other than Z_OK
or
Z_BUF_ERROR
. This means that either the end of the compressed data
stream has been reached (Z_STREAM_END
) or there is an error in the
compressed data. In either of these cases there is no point in continuing
with reading the compressed data, so both loops are terminated.

The second exit point tests if there is any data left in the input buffer,
$input
- remember that the ConsumeInput
option is automatically
enabled when LimitOutput
is used. When the input buffer has been
exhausted, the outer loop can run again and overwrite a now empty
$input
.

ACCESSING ZIP FILES

Although it is possible (with some effort on your part) to use this module
to access .zip files, there are other perl modules available that will
do all the hard work for you. Check out Archive::Zip
,
IO::Compress::Zip
and IO::Uncompress::Unzip
.

CONSTANTS

All the zlib constants are automatically imported when you make use
of Compress::Raw::Zlib.